This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. Primary support for the subproject and the subproject's principal investigator may have been provided by other sources, including other NIH sources. The Total Cost listed for the subproject likely represents the estimated amount of Center infrastructure utilized by the subproject, not direct funding provided by the NCRR grant to the subproject or subproject staff. We observed that CheA[unreadable]289, which is composed of domains P3-P4-P5 of CheA weakly aggregates in solution. In the crystal structure, CheA[unreadable]289 molecules associate with each other via a hydrophobic interface at the end of sub-domain 2 of P5 domain. We use magnetic dilution experiments, disulphide cross-linking experiments and pulsed dipolar ESR to further investigate this binding interface.